Infrapopulation dynamics of Parelaphostrongylus tenuis in white-tailed deer

Abstract

White-tailed deer (Odocoileus virginianus), of known age, collected in northeastern Minnesota (n=379) from November 1991 to May 1993 were examined for Parelaphostrongylus tenuis. Prevalence and intensity estimates were based on adult worms in the cranium and first-stage larvae in the feces of the same individuals. Prevalence of worms in the cranium was higher (82%) than prevalence of larvae in the feces (53%). The difference between these two measures was largely (78%) due to unisexual, occult infections. The spinal column does not seem to be an important site for adult P. tenuis since only one of 26 animals had a worm (immature) located there. In fawns, the prevalence of larvae (35%) and adult worms (68%) was lower than in all older age classes (63%, 89%, respectively). The mean number of adult worms was lower in fawns (2.7) and yearlings (3.0) than in deer 7-15 yr (4.1). Conversely, the mean number of larvae in feces was higher in fawns (102 larvae/g) than in adults 2-6 (36 1/g) and 7-15 yr (36 1/g). More larvae were passed in spring (mean of 77 1/g) than in fall (11 1/g) or winter (38 1/g). Mean fecundity was greater in fawns (52 larvae/g/female worm) than in adults 2-6 yr (15 1/g/f) and 7-15 yr (12 1/g/f). The sex ratio of worms did not change with increasing age of deer, nor did the ratio of worms in the sinuses to subdural space. The number of larvae in feces was not correlated with the number of female P. tenuis in the cranium, but was correlated with the ratio of A smaller sample of white-tailed deer (n = 34) from an area where density reached 30 deer/km2 was compared with animals from the study area where summer density was 3.7 deer/km2. The mean number of adult worms in deer of all ages was similar in both areas (3.2 and 3.5, respectively), but animals in the high density area passed more larvae (94 and 57 1/g, respectively). Results suggest that P. tenuis is long-lived and that deer infected in their first or second summer of life acquire few, if any, additional worms thereafter. A threshold number of adult worms in each deer limits infrapopulation larval production as deer density increases. Infrapopulation larval production, however, is highest in young animals and in the spring. Suprapopulation larval production will be affected by deer density, the proportion of young naive deer in a population and the ability of deer to produce an effective immune response to the parasite.